DYNAMIC CHARACTERIZATION OF A NOVEL EXTERNALLY PRESSURIZED COMPLIANTLY DAMPED GAS-LUBRICATED BEARING WITH HERMETICALLY SEALED SQUEEZE FILM DAMPER MODULES

摘要

Ever-increasing demand for cleaner energy is driving the need for higher power density turbomachinery while reducing cost and simplifying design. Gas lubricated bearings, representing one of the enabling technologies that can help maximize these benefits and have been successfully implemented into turbomachinery applications with rotors weights in the order few kg's. However, load capacity and damping limitations of existing gas bearing technologies prevents the development of larger size oil-free drive trains in the MW power output range. Compliantly damped hybrid gas bearings (CHGB) were introduced as an alternative design to overcome these limitations by providing external pressurization to discrete tilting pads while retaining flexibility in the bearing support to help tolerate misalignment and rotor-pad geometry changes. Additionally, the CHGB concept addresses damping entitlement through the application of bearing support dampers such a metal mesh. An alternative CHGB design, featuring a novel hermetically seal squeeze film damper (HSFD) in the bearing support, was introduced as alternative approach to metal mesh dampers (MMD) to further improve bearing damping. This paper details the rotordynamic characterization of a CHGB with modular HSFD for various operating conditions. Direct and cross-coupled stiffness and damping coefficients are presented for different rotor speeds up to 12,500 rpm, frequencies of excitation between 20-200 Hz, bearing loads between 200-400 lbf, and external hydrostatic pressures reaching 180psi. Direct comparisons to experimental results for a CHGB using (MMD) shows 3X increase in direct damping levels when using HSFD in the compliant bearing support. In addition to the experimental results, an analytical model is presented based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support possessing a pad with 3 degrees of freedom. The numerical results capture the direct stiffness and frequency dependency but underpredict the absolute values for both case when compared to experimental data.